What Does it Mean to Transition?
Many non-cis characters will go through what is called a transition. According to Outright Vermont, a transition is when a person changes their gender expression to match their gender identity. This comes about in a variety of ways.
When writing a character whose gender identity does not match their gender assigned at birth, you must remember that your character may not go through physical transition. That does not mean that they will not go through social transition. Usually, a social transition occurs far in advance of a physical one.
There are stages of physical transition. Some people may start on hormones or hormone blockers, and some will eventually surgically alter the rest of their body. Others may get top surgery, but not bottom surgery, and vice versa. There are a variety of factors into when/if physical transition happens, including personal need and cost. Any physical transition/lack thereof is a completely valid choice for your character to make.
If your character is AFAB and is physically transitioning, they will transition in a different way than an AMAB person. People who were assigned female at birth will usually start off wearing a binder. This usually looks like a tank top that is worn under clothing that flattens out the chest. If your character is a teenager, this is likely what they will start out by doing in terms of physical transition.
If your character is AMAB and is physically transitioning, they will probably begin by changing what clothes they wear, how they shave, and other such things. If you are writing a teen AMAB character, they will likely be doing simple things, like changing their hair and their clothes.
It is rude to ask a trans person if they are going to transition/how far they have transitioned. The only time this could be acceptable to ask is if you are entering into a relationship with a trans person, and only if the trans person is willing to answer you. Therefore, if you have a character who just met a trans person and they are a respectful human, they would not ask this question. Or, they may be in need of a learning experience...
When a social transition occurs, people normally begin by asking those around them to call them by different name and/or pronouns. Pronouns can get confusing, because there are more than just she/her and he/him pronouns. They/them pronouns are now considered to be valid gender-neutral pronouns (you may have noticed that these are the pronouns I have been using when referring to your character), as well as a multitude of others, including ze/zir and ey/em.
Later on in this Playlist we will discuss different pronouns, so don't fret over those too much yet.
No two social transitions are exactly alike, due to family and geographical location. Keep this in mind while writing.
When creating a non-cisgendered character, you must take all of this into consideration. This is complicated stuff, so be sure you know what you are hoping to look for before you begin research. This Playlist's purpose is to help you understand what the possibilities are, so you are able to accurately research and represent the identity your character will have. Remember, stereotypes are not fun for anyone!
Write a short story with a non-cisgender character. Don't outright tell us "Jimmy is a trans boy", but show us through small hints. Remember, as a writer, you want to show, not tell.